A known hydraulic unit for controlling a brake fluid pressure (i.e., hydraulic pressure) applied to a brake apparatus for a vehicle is mainly constituted by a housing on which a power-driven pump and an electromagnetic valve for controlling the hydraulic pressure are assembled. The hydraulic unit controls the hydraulic pressure in a wheel cylinder provided at each wheel of the vehicle by the electromagnetic valve when necessary. In addition, a motor attached to one surface of the housing drives the pump to generate the hydraulic pressure. The hydraulic pressure generated is supplied to the wheel cylinder so as to be used for repressurization after a reduction of the hydraulic pressure or for a braking hydraulic pressure upon automatic braking control.
In order to fix a part or a component such as the electromagnetic valve to the housing in the aforementioned hydraulic unit, a rivet fixing (a caulking) is applied to thereby secure the part to the housing that is plastically deformed. For example, JP3281385B discloses a hydraulic pressure control unit in which a valve housing of an electromagnetic valve is fixed to a housing (which is called a valve receiving body) that is deformed.
Although a downsizing of the hydraulic unit for controlling the brake fluid pressure has been remarkably improved, a further downsizing is strongly desired. Meanwhile, in view of saving weight, an aluminum alloy is commonly used as a material of the housing.
Because densely arranged parts at the housing are inevitable for the purpose of achieving the downsizing of the hydraulic unit, a hole on which a part is assembled (i.e., a part assembly hole) may be forcedly formed adjacent to a part that is rivet-fixed to the housing.
However, when the housing is deformed by the rivet fixing, a force added to the housing at that time is propagated to the part assembly hole formed in the vicinity of the rivet fixing portion, thereby causing the deformation of the part assembly hole. For the housing made of aluminum alloy having lesser strength than an iron-based housing, the propagation of the force is significant. In a case of a large deformation of the part assembly hole, an assembly of the part on the deformed part assembly hole may be interrupted. In addition, in a case where a sliding part such as a piston of a piston pump is assembled on the part assembly hole, the sliding part inserted into the hole may have difficulty sliding smoothly.
According to a current technology, in order to avoid such problem, a sufficient distance is secured between the rivet fixing portion and the part assembly hole of the housing (i.e., a sufficient thickness of the housing is secured between the rivet fixing portion and the part assembly hole). Therefore, a size of the housing increases, which may be a problem for further downsizing a product such as the hydraulic unit.
A need thus exists for a parts assembly which is not susceptible to the drawback mentioned above.